Question

Which of the following compounds is optically inactive?

• A. 2-Chloro-2-methylbutane
• B. 3-Chlorohexane
• C. 2-Chloro-3-methylbutane
• D. 2-Chloropentane

Hint:

When a name features identical locant numbers for two different groups on the same carbon atom (e.g., 2-Chloro-2-methyl), it indicates that two valencies of that carbon are occupied by identical groups, making that center automatically achiral.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
We are tasked with identifying the single alkyl halide compound from the options that is optically inactive due to the absence of an asymmetric chiral carbon center.

Step 2: Detailed Explanation:
A compound is classified as optically active if it contains a chiral carbon atom bonded to four entirely distinct groups. Let's analyze the structures of the options:

3-Chlorohexane: The $\text{C}_3$ position connects to -H, -Cl, an ethyl group, and a propyl group. It is chiral.

2-Chloro-3-methylbutane: The $\text{C}_2$ position connects to -H, -Cl, a methyl group, and an isopropyl group. It is chiral.

2-Chloropentane: The $\text{C}_2$ position connects to -H, -Cl, a methyl group, and a propyl group. It is chiral.

2-Chloro-2-methylbutane: Let us write out its detailed structural configuration around the $\text{C}_2$ central carbon:
$$ \text{CH}_3-\text{C(Cl)(CH}_3)-\text{CH}_2-\text{CH}_3 $$ Inspecting this central carbon ($\text{C}_2$) reveals it is bound to:
1. A chlorine atom (-Cl)
2. An ethyl group ($\text{-CH}_2\text{CH}_3$)
3.

Two identical methyl groups ($\text{-CH}_3$)
Because it contains two identical methyl groups, the central carbon is achiral. This symmetry renders the entire molecule optically inactive.

Step 3: Final Answer: The optically inactive structure is 2-Chloro-2-methylbutane, matching option (A).